Recent pertussis epidemics and fatalities in young infants highlight this disease as a serious re-emerging public health issue. However, no effective therapies exist for treatment of pertussis. Since antibiotic therapy is ineffective (symptoms persist long after bacterial clearance), host-targeted therapeutics may be necessary to treat pertussis disease. A potential host target for this therapy is sphingosine-1- phosphate (S1P) receptor signaling. S1P is a sphingolipid that binds and signals through G protein-coupled receptors (GPCR), and this signaling can attenuate respiratory inflammatory pathology in various models. For instance, treatment with S1P receptor agonists increases pulmonary vascular barrier integrity and reduces lung inflammatory pathology in mouse models of LPS-induced acute lung injury and influenza virus infection. An S1P-related agonist, FTY720, is in use in humans as a therapy for multiple sclerosis, and other related agonists are in advanced clinical trials for a variety of inflammatory diseases, demonstrating the translational potential o this approach. In preliminary studies, we have found that treatment of Bordetella pertussis-infected mice with an S1P receptor agonist soon after bacterial inoculation significantly reduced inflammatory gene expression and lung pathology at the peak of infection. Therefore, we hypothesize that treatment of pertussis-infected mice with S1P receptor agonists will reduce lung inflammatory pathology and that this may represent a novel host-directed therapeutic target for treatment of pertussis. S1P signals through 5 GPCRs that couple to heterotrimeric G proteins of the Gi subclass. Gi proteins are the specific target of modification by pertussis toxin (PT), a major virulence factor of B. pertussis. PT administration in the absence of infection does not cause respiratory pathology, but during infection it inhibits G protein signaling and causes various local and systemic manifestations of pertussis disease. We have shown that PT plays a major role in B. pertussis infection and respiratory pathogenesis through multiple inhibitory effects on host responses to infection. Using adult mouse models to compare respiratory infection by wild type and PT-deficient B. pertussis strains, we found that PT production is associated with exacerbated inflammatory responses at the peak of B. pertussis infection, and that PT prolongs the duration of inflammatory airway pathology. These data indicate that PT may inhibit host mechanisms of attenuating inflammation in the respiratory tract. Based on the known properties of S1P receptor signaling in attenuating inflammatory pathology described above, we hypothesize that S1P can potentially play a role in limiting inflammation during B. pertussis infection, but that PT inhibition of S1P receptor signaling in the lungs prevents this attenuation and exacerbates pertussis inflammatory pathology. In this exploratory/developmental R21 proposal, we will begin to investigate these hypotheses with a long- term goal of developing much needed novel host-targeted therapeutics for pertussis.